Tiltable specimen holder for electron microscopes with electrical deflecting means to wobble the electron beam image



Mar 7, 1967 susuMu OZASA TILTABLE SPECIMEN HOLDER FOR ELECTRONMICROSCOPES WITH ELECTRICAL DEF'LECTING MEANS T0 WOBBLE THE ELECTRONBEAM IMAGE Filed April 7, 1964 6 VIII!!! InuErrrog SUSLIN'IU OzaATTORNEY United States Patent O 3,308,294 TILTABLE SPECIMEN HOLDER FORELECTRON MICROSCOPES WITH ELECTRICAL DEFLECT- ING MEANS T WOBBLE THEELECTRON BEAM IMAGE Susumu Ozasa, Hachioji-shi, Tokyo, Japan, assignorto Hitachi, Ltd, Tokyo, Japan, a corporation of Japan Filed Apr. 7,1964, Ser. No. 357,867 Claims priority, application Japan, May 24, 1963,38/26,292 6 Claims. (Cl. 250-495) This invention relates to electronmicroscopes, and more particularly to specimen tilting devices for usein electron microscopes.

In electron microscopes, specimen tilting devices are used when certainkinds of specimens, particularly crystalline specimens, such as metals,are examined or observed. For example, refer to the Journal ofElectromicroscopy, vol. 12, No. 1, 2-9, 1963, pages 2 through 5. Inusing a specimen tilting device, tilting may be elfected, while watchingthe microscopic image of the specimen on the fluorescent screen. Forbest results, tilting should occur about a particular axis on thespecimen, for example, about the side of the outline of the image orabout a line perpendicular to an internal structure line of thespecimen. For example, see Figure 4 on page 4 of the above-identifiedJournal of Electromicroscopy article. Tilting may also be effected inthe direct-ion of a particular spot in the electron diffraction image.In the tilting device, its tilting axis is fixed in a particulardirection with respect to the microscope housing, or it may be rotatableif a particular direction is selected as a reference starting point. Onthe other hand, the direction of the specimen with respect to themicroscope housing is not constant, and therefore, in known tiltingdevices, the specimen must be rotated so that a particular axis on thespecimen and the tilting axis are coincident with each other.

In electron microscopes employing convention magnetic-field lens, themicroscopic image or the diffraction image will not represent theenlarged image of the specimen directly projected onto the fluorescentscreen, but it usually represents an image which is rotated by a certainangle on. In such case, therefore, the image projected on thefluorescent screen will not indicate the actual posi: tional relation ofthe specimen with respect to the microscope housing. In order to effectthe tilting of the specimen with these known tilting devices, therefore,it is necessary to first measure the angle of rotation of the image andalso the angle formed by the particular axis on the specimen with thetilting axis and then to operate the tilting devices according to thesum or balance of the said two angles. Such an operation of the deviceis complicated and lowers the efficiency of observation. In addition, tothere being involved measurement errors of the two angles, accuratecoincidence of the said both axes is diflicult to obtain. Even if theangles are measured correctly, there is no designation of the tiltingaxis on the fluorescent screen under observation, and there cannot beobtained any confirmation of correct coincidence.

The primary object of the present invention is to provide a specimentilting device for electron microscope having no such defaults ordisadvantages as hereinabove pointed out.

Another object of the present invention is to provide a specimen tiltingdevice of the kind specified in which said tilting operation can beaccomplished without measuring said both angles, and wherein thedirection of the tilting axis can be determined readily by viewing thefluorescent screen.

There are other objects and particularities of the prescut invention,which will be made obvious from the following detailed description ofthe invention, with reference to the accompanying drawings, in which:

FIG. 1 is a longitudinal sectional view of the essential parts of aspecimen tilt-ing device embodying the present invention, and employingan electromagnetic deflecting coil; and

FIG. 2 is a similar view showing another embodiment of the inventionemploying an electrostatic deflecting electrode.

When an electron beam alternately deflecting device, for example, a pairof coils or a ring electrode to which alternating or pulsed voltage orcurrent is applied, is disposed in the direction of a tilting axis ofthe specimen tilting device or alternatively in the directionperpendicular thereto, the electron beam irradiating the specimendisposed in said tilting device is deflected alternately in thedirection of the tilting axis or alternatively in the directionperpendicular thereto. As a consequence, wobbling of the electron beamtakes place in the direction of the alternately deflecting field in themicroscopic image (or the diffraction image) by virtue of the aberrationof the electron lens. This appears to an observer of the fluorescentscreen as a form of modulation. Even though the image might be rotatedmidway in any direction, the direction of the wobbling (or modulation)is always in the direction of the tilting axis, or alternatively, in thedirection perpendicular to the tilting axis depending upon the designused.

In effecting the tilting of the specimen, it is only necessary tooperate so as to bring a desired axis on the specimen into coincidencewith the direction of the wobbling (in the case where the electron beamis deflected alternately in the direction of the tilting axis), or tobring the desired axis on the specimen perpendicular to the direction ofthe wobbling (in the case where the electron beam is alternatelydeflected in the direction perpendicular to the tilting axis). As hasbeen discussed above, since the direction of wobbling (or modulation)indicates the direction of tilting, it is then known that the desiredaxis on the specimen is properly aligned with the tilting axis. Hence,by means of the present invention the desired objective can be obtainedwithout conducting complicated measurements of angles as has beenrequired with known tilting devices.

Further, instead of employing deflecting elements having deflectingeffect laterally to the optical axis as above mentioned, deflectingelements having alternately defleeting effect in the direction oftilting, for example, ringshaped electrodes or ring-shaped coils towhich alternating or pulsed voltage or current is applied, may bedisposed above the specimen and arranged to tilt in unison with thespecimen. In the event that such ring-shaped eletrodes are used, it willresult in the electron beam being deflected alternately above and underthe center axis of the electrode by the pin-hole lens principle as isdescribed in, for example, the Basic Electronics (Kiso Denshi Kogaku)published on October 15, 1960, by the Institute of Electrical Engineersof Japan (Denki Gakkai), pages 21 through 22.

In the event that ring-shaped coils are used, a magnetic field will beproduced in the direction of their center axis. Therefore, so long asthe axis is coincident with the optical axis of the electron microscope,the electron beam will not be deflected. If, however, the center axis ofthe coil is inclined from the optical axis, this will cause the electronbeam to be deflected. It will be apparent from thethree-fingers-of-the-left-hand rule of Fleming that the direction ofthis deflection is perpendicular to the direction obtained in the casewhere the ring-shaped electrode is used.

Accordingly, in the event the specimen is inclined, the electron beamwill be deflected alternately in the direction of the tilting (meaningthe case where the ring-shaped electrode is used) or in a directionperpendicular to the tilting axis, and there takes place wobbling as hasbeen described earlier.-

Referring now to FIG. 1, the specimen tilting device shown comprisesholding means formed by a holder cylinder 2 for specimen 1, tiltingshafts or axes 3, a stationary base 4, and tilting means comprised bytilting supports 5 for holder 2. The foregoing are parts found inconventional devices corresponding, for example, to parts H, D, E, and Fin Figure 2, on page 3 of the Journal of Electromicroscopy articleidentified above. The manner of operation of these parts for effectingtilting is well known and is similar to those stated in theabove-mentioned reference. In addition, coils 6 are provided foralternate deflection, and are mounted on coil supports 7. Coils 6produce magnetic flux in the horizontal direction along the plane ofpaper, which alternately deflects the electron beam to the directionvertical to the paper plane. This direction is made coincident with thedirection of tilting of the specimen 1, which is the directionperpendicular to the tilting axes 3.

The device shown in FIG. 1 may be modified as shown in FIG. 2.Electromagnetic deflecting coils in the former are replaced with anelectrostatic deflecting electrode 8 supported by an insulator 9. Acontact piece 10 is mounted on a contact support 11 and serves to applyan alternating or pulsed electric potential to electrode 8. This resultsin the establishment of a pulsed electric field gradient in the spacebetween electrode 8 and member 2 that can cause deflection of theelectron beam if it is not centered. As long as the specimen 1 is in thezero reference or horizontal position, the electrode 8 is symmetricalwith respect to the optical axis, and there takes place no change in theimage. However when the device is tilted, the center of electrode isdisplaced in the direction of tilting, and the electron beam isalternately deflected in the direction of tilting.

According to the invention as above explained, the orientation oftilting of the specimen or the direction of the axis of tilting on thefluorescent screen can be known direct when the tilting of specimen isbeing adjusted, and consequently, no complicated measurement of anglesis required, and hence no error caused thereby. Further, since thedirection of tilting can be observed on the fluorescent screensimultaneously with the image of specimen, there is no fear at all thattilting will take place in a wrong direction.

What is claimed is:

1. A specimen tilting device for electron microscopes, comprisingholding means for holding the specimen to be examined, tilting meanshaving a tilting axis acting on said holding means for tilting thespecimen, electrical deflecting means physically aligned in a known andfixed manner relative to the tilting axis of said tilting means, andmeans for energizing said electrical deflecting means with analternating electric signal for alternately deflecting the electron beamirradiating said specimen to thereby wobble the image of the electronbeam in a definite direction with respect to the direction of tilting ofsaid specimen.

2. A specimen tilting device for electron microscopes according to claim1, wherein the electrical deflecting means acts in a directionperpendicular to the direction of tilt of the tilting means.

3. A specimen tilting device for electron microscopes according to claim1, in which said electrical deflecting means includes a pair of coils.

4. A specimen tilting device for electron microscopes according to claim1, in which said electrical deflecting means includes a ring-shapedelectrode and wherein with the tilting means in the zero referenceposition the center of said electrode is made coincident with theoptical axis of said electron microscope.

5. A specimen tilting device for electron microscopes comprising:

a supporting member physically supported on the column of an electronmicroscope,

specimen holding means physically supported by said supporting member ina tiltable manner, tilting means acting on said specimen holding meansfor tilting said specimen holding means in a desired direction about atilting axis, electrical deflecting means physically secured to thesupporting member and aligned in a known and fixed manner relative tothe tilting axis of said tilting means, and means for energizing saidelectrical deflecting means with an alternating electric signal foralternately deflecting the electron beam irradiating the specimen tothereby wobble the image of the electron beam in a definite directionwith respect to the direction of tilt.

6. A specimen tilting device for electron microscopes comprising:

a supporting member physically supported on the column of an electronmicroscope,

at tilting support having a tilting axis,

connecting means for movably connecting said tilting support with saidsupporting member,

specimen holding mean-s supported by said tilting support for holding aspecimen irradiated by the electron beam, electrical deflecting meansphysically supported by said holding means and tiltable therewith, andmeans for energizing said electrical defleeting means with continuouslyvarying electrical energy for alternately deflecting said electron beamto thereby wobble the image of the electron beam in a definitedirect-ion with respect to the direction of the tilting axis.

References Cited by the Examiner UNITED STATES PATENTS 2,802,110 8/1957Kazato et al. 250-49.5

RALPH G. NILSON, Primary Examiner.

W. F. LINDQUIST, Assistant Examiner,

1. A SPECIMEN TILTING DEVICE FOR ELECTRON MICROSCOPES, COMPRISINGHOLDING MEANS FOR HOLDING THE SPECIMEN TO BE EXAMINED, TILTING MEANSHAVING A TILTING AXIS ACTING ON SAID HOLDING MEANS FOR TILTING THESPECIMEN, ELECTRICAL DEFLECTING MEANS PHYSICALLY ALIGNED IN A KNOWN ANDFIXED MANNER RELATIVE TO THE TILTING AXIS OF SAID TILTING MEANS, ANDMEANS FOR ENERGIZING SAID ELECTRICAL DEFLECTING MEANS WITH ANALTERNATING ELECTRIC SIGNAL FOR ALTERNATELY DEFLECTING THE ELECTRON BEAMIRRADIATING SAID SPECIMEN TO THEREBY WOBBLE THE IMAGE OF THE ELECTRONBEAM IN A DEFINITE DIRECTION WITH RESPECT TO THE DIRECTION OF TILTING OFSAID SPECIMEN.